Some tubular linear motors used in elevators comprise a mobile tubular primary element and a stationary rod-shaped secondary element which passes through the primary element. The secondary element comprises a magnetic conductor having an outer surface coated with a nonmagnetic conductor made of aluminum, copper, or the like. An air gap is formed between the primary and secondary elements.
The typical primary element is shown in FIGS. 9-11. As shown in FIGS. 10a and 10b, a plurality of slots 8 are cut on a thin plate made of magnetic material to form a comb-shaped core plate 4 having teeth 13. As shown in FIGS. 11a and b, the core plates are laminated and welded to a side plate 14 and a back plate 15 to form an integrated core group 5. Referring to FIG. 9a, a plurality of core groups 5 are set equidistantly in a radial configuration with slots 8 facing toward the secondary element 2. A pair of end flanges (i.e., "caps") are used to clamp the core groups with the aid of a plurality of bolts 7 and nuts (not shown) to form the primary element 1. A plurality of freely rotating wheels 12 is set in the end flanges to maintain the air gap between the primary and secondary elements. In each slot 8 a coil 9 is set.
However, as the laminated core plates are welded to the side plate and back plate, curving or twisting of the core group may occur which may distort the air gap after the core groups are assembled. Further, the parallelism between the two end surfaces of the core group is degraded; hence, when fastening is carried out using the nuts, a play is formed for the shorter core group. In consideration of this problem, the following measures are taken:
a) The core groups are annealed to eliminate the curve and twist;
b) The back sheet and the side sheet are thicker and stronger so as to suppress the distortion caused by welding; and
c) After welding, machining is required to correct the curve of the circle of the core group, the parallelism between the two end planes, and the desired total length of the primary element.